Recovery of metallocene complexes

ABSTRACT

Metallocene complexes of the formula I ##STR1## where M is titanium, zirconium, hafnium, vanadium, niobium or tantalum, 
     n is an integer from 0 to 10, 
     R 5  is ##STR2##  R 11  to R 14  are as designated in the disclosure, n 1  is an integer from 0 to 10, 
     X 1  to X 4  are each fluorine, chlorine, bromine, iodine, hydrogen, C 1  -C 10  -alkyl, C 6  -C 15  -aryl, alkylaryl having 1 to 10 carbon atoms in the alkyl radical and 6 to 20 carbon atoms in the aryl radical, --OR 15  --, --NR 15  R 16  or ##STR3##  R 15  to R 21  are as designated in the disclosure, and o, p, q, r are each an integer from 0 to 4, the sum o+p+q+r+1 corresponding to the valency of M, 
     which were used as active catalyst components in the preparation of polymers of C 2  -C 10  -alkenes, are recovered by a process wherein the polymerization is stopped by adding an acid and the metallocene complexes of the formula I are recovered by extraction from the reaction mixture.

This application is a divisional of prior application Ser. No. 08/847,487, filed Apr. 25, 1997, now U.S. Pat. No. 5,840,949.

The present invention relates to processes for recovering metallocene complexes of the general formula I ##STR4## where M is titanium, zirconium, hafnium, vanadium, niobium or tantalum,

R¹ to R⁴ are each hydrogen, C₁ -C₁₀ -alkyl, 5-7-membered cycloalkyl which in turn may carry C₁ -C₁₀ -alkyl as a substituent, C₆ -C₁₅ -aryl or arylalkyl, and two adjacent radicals together may furthermore form a cyclic group of 4 to 15 carbon atoms, Si(R⁶)₃, ##STR5## R⁶ is C₁ -C₁₀ -alkyl, C₆ -C₁₅ -aryl or C₃ -C₁₀ -cycloalkyl,

R⁷ and R⁸ are each hydrogen, C₁ -C₁₀ -alkyl, C₆ -C₁₅ -aryl or C₃ -C₁₀ -cycloalkyl,

R⁹ and R¹⁰ are each C₁ -C₁₀ -alkyl, C₆ -C₁₅ -aryl or C₃ -C₁₀ -cycloalkyl,

Y is nitrogen, phosphorus, arsenic, antimony or bismuth,

Z is oxygen, sulfur, selenium or tellurium,

n is an integer from 0 to 10,

R⁵ is ##STR6## R¹¹ and R¹² are each hydrogen, C₁ -C₁₀ -alkyl, C₆ -C₁₅ -aryl or C₃ -C₁₀ -cycloalkyl,

R¹³ and R¹⁴ are each, C₁ -C₁₀ -alkyl, C₆ -C₁₅ -aryl or C₃ -C₁₀ -cycloalkyl,

n¹ is an integer from 0 to 10,

X¹ to X⁴ are each fluorine, chlorine, bromine, iodine, hydrogen, C₁ -C₁₀ -alkyl, C₆ -C₁₅ -aryl, alkylaryl having 1 to 10 carbon atoms in the alkyl radical and 6 to 20 carbon atoms in the aryl radical, --OR¹⁵ --, --NR¹⁵ R¹⁶ or ##STR7## R¹⁵ and R¹⁶ are each C₁ -C₁₀ -alkyl, C₆ -C₁₅ -aryl, alkylaryl, arylalkyl, fluoroalkyl or fluoroaryl, each having 1 to 10 carbon atoms in the alkyl radical and 6 to 20 carbon atoms in the aryl radical,

R¹⁷ to R²¹ are each hydrogen, C₁ -C₁₀ -alkyl, 5-7-membered cycloalkyl which in turn may carry C₁ -C₁₀ -alkyl as a substituent, C₆ -C₁₅ -aryl or arylalkyl, and two adjacent radicals together may furthermore form a cyclic group of 4 to 15 carbon atoms, Si(R²²)₃, ##STR8## R²² is C₁ -C₁₀ -alkyl, C₆ -C₁₅ -aryl or C₃ -C₁₀ -cycloalkyl,

R²³ and R²⁴ are each hydrogen, C₁ -C₁₀ -alkyl, C₆ -C₁₅ -aryl or C₃ -C₁₀ -cycloalkyl,

R²⁵ and R²⁶ are each C₁ -C₁₀ -alkyl, C₆ -C₁₅ -aryl or C₃ -C₁₀ -cycloalkyl,

n² is an integer from 0 to 10 and

o, p, q, r are each an integer from 0 to 4, the sum o+p+q+r+1 corresponding to the valency of M,

which were used as active catalyst components in the preparation of polymers of C₂ -C₁₀ -alkenes.

The present invention furthermore relates to the use of the recovered metallocene complexes for the preparation of polymers of C₂ -C₁₀ -alkenes and to processes for the preparation of these polymers.

The use of metallocene complexes as active catalyst components for the preparation of polyolefins is known. A large number of industrial polymerization processes were developed, in which however the metallocene complex remains in the polymer prepared. However, the polymer is thus contaminated with the metallocene complex and in addition the expensive metallocene complex is lost in this manner.

It is an object of the present invention to provide a process for recovering metallocene complexes.

We have found that this object is achieved by processes for recovering metallocene complexes of the general formula I which were used as active catalyst components in the preparation of polymers of C₂ -C₁₀ -alkenes, wherein the polymerization is stopped by adding an acid and the metallocene complexes of the general formula I are recovered by extraction from the reaction mixture.

We have also found the use of the recovered metallocene complexes for the preparation of polymers of C₂ -C₁₀ -alkenes and processes for the preparation of these polymers.

Preferred metallocene complexes of the general formula I which are used in the novel process are those in which

M is titanium, zirconium or hafnium, in particular titanium,

R¹ to R⁴ are each hydrogen, C₁ -C₆ -alkyl or C₆ -C₁₅ -aryl, in particular hydrogen, or two adjacent radicals may form a cyclic group of 8 to 12 carbon atoms,

R⁵ is ##STR9## R¹¹ and R¹² are each hydrogen or C₁ -C₄ -alkyl, in particular hydrogen, methyl or ethyl,

R¹³ and R¹⁴ are each C₁ -C₆ -alkyl, in particular methyl, ethyl, n-propyl, isopropyl, n-butyl or tert-butyl, or phenyl,

n¹ is an integer from 1 to 4,

Y is nitrogen or phosphorus,

Z is oxygen or sulfur,

X¹ to X⁴ are each chlorine, C₁ -C₄ -alkyl or ##STR10## R¹⁷ to R²¹ are each hydrogen, C₁ -C₆ -alkyl or C₆ -C₁₅ -aryl, or two adjacent radicals may form a cyclic group of 8 to 12 carbon atoms, Si(R²²)₃ or ##STR11## R²² is C₁ -C₁₀ -alkyl, preferably C₁ -C₄ -alkyl, R²³ and R²⁴ are each hydrogen or C₁ -C₄ -alkyl, in particular hydrogen, methyl or ethyl,

R²⁵ and R²⁶ are each C₁ -C₆ -alkyl, in particular methyl, ethyl, n-propyl, isopropyl, n-butyl or tert-butyl, or phenyl and

n² is an integer from 1 to 4.

Particularly preferred metallocene complexes of the general formula I are those in which R⁵ is ##STR12## in particular ##STR13## and R¹ to R⁴ are each hydrogen. It is also particularly preferable if M is titanium, if X¹, X² and X³ are each chlorine, o, p and q are each 1 and r is 0 or if X¹ and X² are each chlorine and X³ is ##STR14## where R¹⁷ to R²⁰ are each hydrogen and R²¹ is trimethylsilyl, and o, p and q are each 1 and r is 0.

Examples of particularly preferred metallocene complexes of the general formula I are:

Trichloro-η⁵ - 2-(N,N-diisopropylammonium)ethylcyclopentadienyl!-titanium(IV) chloride

Dichloro-di-{η⁵ - 2-(N,N-diisopropylammonium)ethylcyclopentadienyl!}-titanium(IV) dichloride

Trichloro-η⁵ - 2-(N,N-diisopropylammonium)ethylcyclopentadienyl!-zirconium(IV) chloride

Dichloro-di-{η⁵ - 2-(N,N-diisopropylammonium)ethylcyclopentadienyl!}-zirconium(IV) dichloride

Trichloro-η⁵ - 2-(N,N-dimethylammonium)ethylcyclopentadienyl!-titanium(IV) chloride

Dichloro-di-{η⁵ - 2-(N,N-dimethylammonium)ethylcyclopentadienyl!}-titanium(IV) dichloride

Trichloro-η⁵ - 2-(N,N-dimethylammonium)ethylcyclopentadienyl!-zirconium(IV) chloride

Dichloro-di-{η⁵ - 2-N,N-dimethylammonium)ethylcyclopentadienyl!}-zirconium(IV) dichloride

Dichloro-η⁵ - 2-(N,N-diisopropylammonium)ethylcyclopentadienyl!-(trimethylsilyl-cyclopentadienyl)-titanium(IV) chloride

Dichloro-η⁵ - 2-(N,N-diisopropylammonium)ethylcyclopentadienyl!-(trimethylsilylcyclopentadienyl)-zirconium(IV) chloride

Dichloro-cyclopentadienyl-η⁵ - 2-(N,N-diisopropylammonium)ethylcyclopentadienyl!-titanium(IV) chloride

Dichloro-cyclopentadienyl-η⁵ - 2-(N,N-diisopropylammonium)ethylcyclopentadienyl!-zirconium(IV) chloride

Mixtures of different metallocene complexes I may also have been used.

The metallocene complexes I can be prepared by first preparing the cyclopentadienyl systems functionalized with a heteroatom by reaction of cyclopentadienyllithium or cyclopentadienylsodium with the chloroalkane functionalized with a heteroatom, as described in J. Organometal. Chem. 423 (1992), 31-38, and J. Organometal. Chem. 480 (1994) C18-C19. The corresponding cyclopentadienyl lithium systems functionalized with the heteroatom can then be prepared by reacting the cyclopentadienyl systems functionalized with the heteroatom with alkyllithium, for example n-butyllithium, for example as described in J. Organometal. Chem. 486 (1995), 287-289. These can then preferably be reacted with MCl₄ to give the corresponding metallocene complexes, as described in J. Organometal. Chem. 486 (1995), 287-289, although the metallocene complexes do not as yet carry cationically functionalized cyclopentadienyl ligands. The conversion into the metallocene complexes of the general formula I can be effected by adding acids of any type, as described in J. Organometal. Chem. 486 (1995) 287-289.

The addition of these acids gives an ion which has the opposite sign to the metallocene complexes of the general formula I and is derived from the type of acid added. These opposite ions may be, for example, halides, carboxylic acid anions, sulfates, phosphates, carbonates, nitrates, PF₆ ⁻, BF₄ ³¹ or HPO₄ ²⁻. The type of opposite ion is not critical. Halides are preferred, in particular chlorides.

In the novel process for recovering metallocene complexes of the general formula I, these metallocene complexes were used as active catalyst components in the preparation of polymers of C₂ -C₁₀ -alkenes. The catalyst systems used also contain, as a further active component, compounds forming metallocenium ions.

Suitable compounds forming metallocenium ions are in particular strong, neutral Lewis acids, ionic compounds having Lewis acid cations, ionic compounds having Bronsted acids as cations and alumoxane compounds.

Preferred strong, neutral Lewis acids are compounds of the general formula IV

    M.sup.1 X.sup.5 X.sup.6 X.sup.7                            IV

where

M¹ is an element of main group III of the Periodic Table, in particular B, Al or Ga, preferably B, and

X⁵, X⁶ and X⁷ are each hydrogen, C₁ -C₁₀ -alkyl, C₆ -C₁₅ -aryl, alkylaryl, arylalkyl, haloalkyl or haloaryl, each having 1 to 10 carbon atoms in the alkyl radical and 6 to 20 carbon atoms in the aryl radical, or fluorine, chlorine, bromine or iodine, in particular haloaryl, preferably pentafluorophenyl.

Particularly preferred compounds of the general formula IV are those in which X⁵, X⁶ and X⁷ are identical, preferably tris(pentafluorophenyl)borane.

Suitable ionic compounds having Lewis acid cations are compounds of the general formula v

     (A.sup.a+)Q.sub.1 Q.sub.2 . . . Q.sub.z !.sup.d+          V

where

A is an element of main groups I to VI or of subgroups I to VIII of the Periodic Table,

Q₁ to Q_(z) are radicals having a single negative charge, such as C₁ -C₂₈ -alkyl, C₆ -C₁₅ -aryl, alkylaryl, arylalkyl, haloalkyl, haloaryl, each having 6 to 20 carbon atoms in the aryl radical and 1 to 28 carbon atoms in the alkyl radical, or C₁ -C₁₀ -cycloalkyl which may be substituted by C₁ -C₁₀ -alkyl, or halogen, C₁ -C₂₈ -alkoxy, C₆ -C₁₅ -aryloxy, silyl or mercaptyl,

a is an integer from 1 to 6,

z is an integer from 0 to 5 and

d corresponds to the difference a-z, but d is greater than or equal to 1.

Carbonium cations, oxonium cations and sulfonium cations and cationic transition metal complexes are particularly suitable. Particular examples are the triphenylmethyl cation, the silver cation and the 1,1'-dimethylferrocenyl cation. They preferably have noncoordinating opposite ions, in particular boron compounds, as also stated in WO 91/09882, preferably tetrakis(pentafluorophenyl)borate.

Ionic compounds having Bronsted acids as cations and preferably also noncoordinating opposite ions are mentioned in WO 91/09882, the preferred cation being N,N-dimethylanilinium.

Particularly suitable compounds forming metallocenium ions are open-chain or cyclic alumoxane compounds of the general formula II or III ##STR15## where R²⁷ is C₁ -C₄ -alkyl, preferably methyl or ethyl, and m is an integer from 5 to 30, preferably from 10 to 25.

The preparation of these oligomeric alumoxane compounds is usually carried out by reacting a solution of the trialkylaluminum with water and is described, inter alia, in EP-A 284 708 and U.S. Pat. No. 4,794,096.

As a rule, the oligomeric alumoxane compounds obtained are present as mixtures of both linear and cyclic chain molecules of different lengths so that m is to be regarded as an average value. The alumoxane compounds may also be present as a mixture with other metal alkyls, preferably with alkylaluminum.

Aryloxyalumoxanes as described in U.S. Pat. No. 5,391,793, aminoalumoxanes as described in U.S. Pat. No. 5,371,260, aminoalumoxane hydrochlorides as described in EP-A 633 264, silyloxyalumoxanes as described in EP-A 621 279 or mixtures thereof may furthermore be used as compounds forming metallocenium ions.

It has proven advantageous to use the metallocene complexes and the oligomeric alumoxane compound in amounts such that the atomic ratio of aluminum from the oligomeric alumoxane compound to the transition metal from the metallocene complexes is from 10:1 to 10⁶ :1, in particular from 10:1 to 10⁴ :1.

Aromatic hydrocarbons, preferably of 6 to 20 carbon atoms, in particular xylenes and toluene and mixtures thereof, are usually used as solvents for these catalyst systems.

The catalyst systems used in the novel recovery process may also have been used in supported form.

Preferably used carriers are finely divided carriers which preferably have a particle diameter of from 1 to 300 μm, in particular from 30 to 70 μm. Examples of suitable carriers are silica gels, preferably those of the formula SiO₂. a Al₂ O₃, where a is from 0 to 2, preferably from 0 to 0.5; these are therefore aluminosilicates or silica. Such products are commercially available, for example Silica Gel 332 from Grace. Further carriers include finely divided polyolefins, for example finely divided polypropylene, or magnesium chloride.

In the novel process for recovering metallocene complexes of the general formula I, these metallocene complexes have already been used for the preparation of polymers of C₂ -C₁₀ -alkenes. This polymerization can be carried out in the gas phase, in suspension, in solution or in liquid monomers. Examples of suitable suspending agents are aliphatic hydrocarbons. The novel process is preferably carried out in solution, preferably in toluene as the solvent.

Here, it has proven particularly preferable if the metallocene complex of the general formula I (with its opposite ion) is suspended in toluene at from -80 to 110° C., and the compound forming metallocenium ions, likewise preferably as a solution in toluene, is added at from 0.5 to 50 bar. The actual polymerization conditions are not critical per se, temperatures of from -50 to 300° C., pressures of from 0.5 to 3000 bar and reaction times of from 0.1 to 24 hours being preferred.

The average molar mass of the resulting polymer can be controlled by the methods usually used in polymerization technology, for example by adding regulators such as hydrogen.

Suitable C₂ -C₁₀ -alkenes which may be used for the polymerization are in particular ethylene as well as propylene and higher alk-1-enes, such as but-1-ene, pent-1-ene and hex-1-ene. The term polymers is understood as meaning both homopolymers and copolymers.

The metallocene complexes of the general formula I can be recovered by the novel process by stopping the polymerization by adding an acid and recovering the metallocene complex of the general formula I by extraction from the reaction mixture.

Suitable acids are compounds of any type in which the anion is capable of stabilizing the metallocene cation at the metal M; preferably, the anion forms a bond with the metallocene cation at the metal M. Preferred acids are inorganic acids, such as hydrohalic acids, in particular HCl. However, it is also possible to use organic acids, such as carboxylic acids, for example acetic acid, or substituted carboxylic acids, such as trifluoroacetic acid, or mixtures of different acids.

The acids may be used in concentrated form or as an aqueous and/or alcoholic solution.

The amount of acid is not critical per se, and a molar ratio of acid to metallocene complex of from 10000000:1 to 3:1, in particular from 500000:1 to 1000:1, may be used.

It has proven preferable to add the acid at room temperature and ambient pressure, it is also possible to employ temperatures of from -80 to 200° C. and pressures of from 0.1 to 300 bar.

The extraction is usually carried out in a solvent, and all solvents known per se and suitable for the extraction may be used. Suitable solvents are, for example, water, aromatic hydrocarbons, such as toluene, halohydrocarbons, in particular chlorohydrocarbons, such as chloroform or dichloromethane, ethers, such as diethyl ether or tetrahydrofuran, or alcohols, such as methanol. Mixtures of different solvents may also be used. The type of solvent depends on the type of metallocene complex. However, dichloromethane is preferably used.

The amounts of solvent used for the extraction and the temperature and the pressure are not critical per se. The amount of solvent may be from 1 l to 0.1 l, based on 1 mmol of metallocene complex, the temperature may be from 20 to 150° C. and the pressure may be from 0.1 to 300 bar.

After the extraction, the recovered metallocene complex of the general formula I can be isolated as a solid by removing the solvent and, if required, washing the metallocene complex.

The metallocene complexes of the general formula I which are recovered by the novel process can be reused as active catalyst components for the preparation of polymers of C₂ -C₁₀ -alkenes. Details in this context are surplus since the metallocene complex recovered can be used similarly to the freshly prepared metallocene complex, and reference may therefore be made to existing publications.

Here too, a compound forming metallocenium ions (component B)) is used as a further active catalyst component and the polymerization process corresponds to that already described, it being possible to stop the polymerization by adding acids. The novel process for recovering metallocene complexes of the general formula I can be carried out several times, preferably up to 10 times, in succession. It is also possible to use mixtures of a plurality of recovered metallocene complexes of the general formula I or mixtures of recovered metallocene complex and fresh metallocene complex, said complexes preferably having the same chemical structure. The ratio of recovered metallocene complex to fresh metallocene complex may be varied within any desired limits.

When recovered metallocene complex of the general formula I is used for the preparation of polymers of C₂ -C₁₀ -alkenes, ethylene is likewise a preferred monomer, as described above.

The novel process for recovering metallocene complexes is technically simple to carry out, the expensive complexes can be reused without expensive working up, the productivities of the catalyst systems which contain recovered metallocene complexes as active catalyst components are comparable with the productivities of catalyst systems which contain fresh metallocene complexes as active catalyst components, and the polymers formed are not contaminated with metallocene complexes and moreover have properties which correspond to those of polymers which were prepared by means of fresh metallocene complexes.

EXAMPLES Examples 1 and 2: Preparation of the metallocene complexes I Example 1: Preparation of ##STR16##

A solution of 20.2 mmol of I' ##STR17## in 80 ml of diethyl ether (prepared from 3.90 g (20.2 mmol) of I* ##STR18## and 12.60 ml (20.2 mmol) of a 1.6 molar solution of n-butyllithium in diethyl ether) was added dropwise at -40° C. to a solution of 1.92 g (10.1 mmol) of TiCl₄ in 80 ml of toluene. Thereafter, the reaction mixture was allowed to warm up to room temperature in the course of 6 hours and was stirred for a further 10 hours. The precipitated solid was separated off by decanting and the residue was washed with 2×30 ml of cold (-40° C.) pentane. A deep red solid was obtained. Recrystallization from toluene gave red crystals. Yield: 2.50 g (49%). M.p.: 156° C. (decomposition).

¹ H-NMR (CDCl₃): δ=0.92 (d, ³ J=6.5 Hz, 24H, CH--CH₃), 2.62 (m, 4H, Cp--CH₂), 2.69 (m, 4H, N--CH₂), 2.99 (m, 4H, CH--CH₃), 6.32-6.36 (m, 8H, Cp--H). ¹ H-NMR (C₆ D₆): δ=0.90 (d, ³ J=6.6 Hz, 24H, CH--CH₃), 2.60 (m, 4H, Cp--CH₂), 2.93 (m, 8H, N--CH₂, CH--CH₃), 5.76 (m, 4H, Cp--H), 6.13 (m, 4H, Cp--H).

¹³ C-NMR (C₆ D₆): δ=21.0 (CH--CH₃), 33.1 (Cp--CH₂), 45.6 (CH₂ --N), 48.2 (CH--CH₃), 114.6, 122.9 (Ring--CH═), 136.7 (Ring═C--CH₂ --CH₂).

MS (LSIMS) m/z (rel. Int. %)!: 503 (3) M⁺ +1H!, 468 (3) M⁺ -2Cl!, 114 (100) i(C₃ H₇)₂ NCH₂ CH₂ ⁺ !, 65 (8) C₅ H₅ ⁺ !.

CHN: C₂₆ H₄₄ Cl₄ N₂ Zr(503.43). Calculated: C 62.03 H 8.80 N 5.56 Found: C 61.92 H 8.68 N 5.43

Cl analysis (according to Schoninger) Calculated: 14.08 Found: 12.97

15 ml of HCl-saturated methanol solution were added to 550 mg (1.09 mmol) of this product and stirring was carried out for 30 minutes. Removal of the solvent under reduced pressure gave a reddish brown solid. Yield: 628 mg (quantitative). M.p.: 144° C. (decomposition).

¹ H-NMR (CD₃ OD): δ=1.39, 1.40 (2d, ³ J=6.6 Hz, 24H, CH--CH₃), 3.33 (m, 4H, Cp--CH₂), 3.56 (m, 4H, N--CH₂), 3.78 (m, 4H, CH--CH₃), 6.44 (m, 4H, Cp--H), 6.74 (m, 4H, Cp--H).

¹³ C-NMR (CD₃ OD): δ=17.2, 18.8 (CH--CH₃), 29.2 (Cp--CH₂), 47.3 (CH₂ --N), 56.5 (CH--CH₃), 115.8, 125.1 (Ring--CH═), 132.6 (Ring--CH═), 132.6 (Ring═C--CH₂ --CH₂).

CHN: C₂₆ H₄₆ Cl₄ N₂ Ti (576.35). Calculated:C 54.18 H 8.04 N 4.86 Found: C 53.89 H 8.30 N 4.72

Cl analysis (according to Schoninger) Calculated: 24.60 Found: 26.33

Example 2: Preparation of ##STR19##

A solution of 3.43 mmol of I' in 20 ml of diethyl ether (prepared from 0.66 g (3.43 mmol) of I* and 2.14 ml (3.43 mmol) of a 1.6 molar solution of n-butyllithium in hexane) was added dropwise at -30° C. to a solution of 1 g (3.43 mmol) of (η⁵ --C₅ H₄ Si(CH₃)₃)TiCl₃ in 40 ml of toluene. Thereafter, the reaction mixture was allowed to warm up to room temperature in the course of 1 hour and was stirred for a further 5 hours. The precipitated solid was separated off by decanting and the residue was washed with 2×20 ml of cold pentane. An orange-red solid was obtained. Yield: 0.82 g (53%), m.p.: 170° C.

¹ H-NMR(C₆ D₆): δ=0.30 (s, 9H, Si--CH₃), 0.89 (d, ³ J=5.5 Hz, 12H, CH--CH₃), 2.61 (m, 2H, Cp--CH₂), 2.93 (m, 4H, N--CH₂, CH--CH₃), 5.74, 6.12 (2m, 4H, Cp--H), 5.97, 6.46 (2m, 4H, Cp--H).

¹³ C-NMR(C₆ D₆): δ=0.10 (Si--CH₃), 21.0 (CH--CH₃), 32.9 (Cp--CH₂), 45.6 (CH₂ --N), 48.2 (CH--CH₃), 114.0, 124.3 (Cp--C), 119.1, 129.3 (Cp--C).

²⁹ Si-NMR (C₆ D₆): δ=-6.8 (Si--CH₃).

MS (CI) m/z (rel. Int. %)!: 448 (0,5) M⁺ !, 413 (1) M⁺ -Cl!, 377 (5) M⁺ -2Cl!, 114 (100) i-(C₃ H₇)₂ NCH₂ ⁺ !.

CHN: C₂₁ H₃₅ Cl₂ NTiSi (448.38) Calculated: C 56.25 H 7.86 N 3.12 Found: C 56.34 H 7.48 N 2.41

10 ml of HCl-saturated methanol solution were added to 350 mg (0.73 mmol) of this product and stirring was carried out for 30 minutes. After removal of the solvent under reduced pressure, the residue was washed with 2×20 ml of diethyl ether. A red, amorphous, very hygroscopic solid was obtained. Crystallization from CH₂ Cl₂ /toluene gave red crystals. Yield: 300 mg (0.62 mmol, 85%). M.p.: 163° C. (decomposition).

¹ H-NMR (CD₃ OD): δ=0.25 (s, 9H, Si--CH₃), 1.40, 1.41 (2d, ³ J=6.6 Hz, 12H, CH--CH₃), 3.30 (m, 2H, Cp--CH₂), 3.60 (m, 2H, N--CH₂), 3.77 (m, 2H, CH--CH₃), 6.36 (t, ³ J=2.7 Hz, 2H, Cp--H), 6.76 (t, ³ J=2.5 Hz, 2H, Cp--H), 6.71 (t, ³ J=2.5 Hz, 2H, Cp--H), 6.93 (t, ³ J=2.5 Hz, 2H, Cp--H).

¹ H-NMR (CD₃ CN): δ=0.23 (s, 9H, Si--CH₃), 1.35, 1.42 (2d, ³ J=6.6 Hz, 12H, CH--CH₃), 3.36 (m, 4H, Cp--CH₂, N--CH₂), 3.63 (m, 2H, CH--CH₃), 6.36 (t, ³ J=2.6 Hz, 2H, Cp--H), 6.60 (t ³ J=2.7 Hz, 2H, Cp--H), 6.70 (t, ³ J=2.5 Hz, 2H, Cp--H), 6.92 (t, ³ J=2.6 Hz, 2H, Cp--H).

¹ H-NMR (CDCl₃): δ=0.21 (s, 9H, Si--CH₃), 1.41, 1.49 (2d, ³ J=6.6 Hz, 12H, CH--CH₃), 3.50 (m, 4H, Cp--CH₂, N--CH₂), 3.64 (m, 2H, CH--CH₃), 6.23 (t, ³ J=2.6 Hz, 2H, Cp--H), 6.42 (t, ³ J=2.6 Hz, 2H, Cp--H), 6.61 (t, ³ J=2.3 Hz, 2H, Cp--H), 6.85 (t, ³ J=2.6 Hz, 2H, Cp--H), 11.2 (br. m, 1H, N--H).

¹³ C-NMR (CD₃ OD): δ=0.0 (Si--CH₃), 17.4, 19.0 (CH--CH₃), 29.2 (Cp--CH₂), 47.6 (CH₂ --N), 56.7 (CH--CH₃), 114.7, 126.5, 131.9 (Cp--C), 122.4, 130.1, 134.7 (Cp--C).

²⁹ Si-NMR (CD₃ OD): δ=-6.09 (Si--CH₃),

CHN: C₂₁ H₃₆ Cl₃ NTiSi (484.84) Calculated: C 52.02 H 7.48 N 2.88 Found: C 52.50 H 8.02 N 2.93

Examples 3 and 4: Preparation of polyethylene (PE) using fresh metallocene complex and recovery of the metallocene complex

The metallocene complexes I1 and I2 (from Examples 1 and 2) were each suspended in toluene at room temperature. Under an ethylene atmosphere (1 bar), a 10% strength solution of methylalumoxane (MAO) in toluene was added dropwise in each case. After 5 minutes, the solution slowly became cloudy as a result of the formation of PE and warmed up. After a reaction time, the polymerization was stopped by adding 500 ml of methanolic/aqueous HCl (400 ml of methanol, 100 ml of concentrated HCl). The PE was filtered off, washed with water and acetone in Example 3 and with dilute HCl and water in Example 4 and dried until the weight was constant. The filtrate was evaporated to dryness and the residue was extracted with dichloromethane (in a Soxhlet apparatus in Example 4). After removal of the solvent and washing with diethyl ether, the respective metallocene complex was isolated as a solid.

Examples 5 and 6: Preparation of PE using recovered metallocene complex

The procedure was as in Examples 3 and 4, except that the metallocene complexes I1 and I2 were metallocene complexes I1W and I2W recovered from Examples 3 and 4. After the polymerization had been stopped by adding 500 ml of methanolic/aqueous HCl as in Examples 3 and 4, the PE was filtered off, washed with water and acetone and dried until the weight was constant.

Comparative Examples V1 and V2: Preparation of PE using fresh metallocene complex

The procedure was as in Examples 5 and 6, except that the metallocene complexes I1 and I2 used were fresh metallocene complexes (from Examples 1 and 2).

The amounts of starting materials, the reaction times and the properties of the resulting polyethylenes are summarized in the table below.

The η value was determined according to ISO 1628-3, and the weight average values M_(w) and number average values M_(n) by means of gel permeation chromatography.

                                      TABLE     __________________________________________________________________________                            Dichloro                                 Extrac                                     Yield of  Productivity     Exam        Metallocene              Toluene  Reaction                            methane                                 tion                                     metallocene                                           Yield                                                g of PE/mol                                                     η value     ple        complex               ml!                  MAO  time  h!                             ml! time  h!                                     complex                                           of PE                                               xc(C.sub.2 H.sub.4)xh!                                                      dl/g!                                                         M.sub.w                                                             M.sub.n                                                                M.sub.w                                                                /M.sub.n     __________________________________________________________________________     3  600 mg I1              40  63 ml                       1    150  0.5 orange-red                                           11.0 g                                               0.88 × 10.sup.4                                                     0.18                                                          4300                                                             1077                                                                4.0        (1.04 mmol)                  (0.104             380 mg                  mol)               (63%)     4  1000 mg I2              40  124 mol                       1    300  5   red   5.3 g                                               0.26 × 10.sup.4                                                     0.56                                                          3834                                                             1493                                                                2.6        (2.06 mmol)                  (0.21 mol)         730 mg                                     (73%)     5  23 mg I1W               5  12 ml                       4    --   --  --    1.7 g                                               1.0 × 10.sup.4                                                     0.68                                                         15836                                                             4613                                                                3.8        (40 μmol)                  (20 mmol)     6  42 mg I2W              20  26 ml                       3    --   --  --    3. g                                               1.2 × 10.sup.4                                                     0.33                                                         14356                                                             4708                                                                3.1        (86.6 μmol)                  (43.3                  (mmol)     V1 23 mg I1               5  12 ml                       4    --   --  --    1.7 g                                               1.0 × 10.sup.4                                                     0.78                                                         14621                                                             3661                                                                4.0        (40 μmol)                  (20 mmol)     V2 42 mg I2              20  26 ml                       3    --   --  --    3.0 g                                               1.2 × 10.sup.4                                                     0.38                                                         15237                                                             5185                                                                2.9        (86.6 μmol)                  (43.3                  mmol)     __________________________________________________________________________ 

We claim:
 1. A process for the preparation of polymers of C₂ -C₁₀ -alkenes by polymerizing C₂ -C₁₀ -alkenes at temperatures of from about -50 to about 300° C. and pressures of from about 0.5 to about 3000 bar in the presence of a catalyst system, wherein the catalyst system used is one which contains, as active components,A) a metallocene complex of the formula I, ##STR20## where M is titanium, zirconium, hafnium, vanadium, niobium or tantalum,R¹ to R⁴ are each hydrogen, C₁ -C₁₀ -alkyl, 5-7-membered cycloalkyl which in turn may carry C₁ -C₁₀ -alkyl as a substituent, C₆ -C₁₅ -aryl or arylalkyl, and two adjacent radicals together may furthermore form a cyclic group of 4 to 15 carbon atoms, Si(R⁶)₃, ##STR21## R⁶ is C₁ -C₁₀ -alkyl, C₆ -C₁₅ -aryl or C₃ -C₁₀ -cycloalkyl, R⁷ and R⁸ are each hydrogen, C₁ -C₁₀ -alkyl, C₆ -C₁₅ -aryl or C₃ -C₁₀ -cycloalkyl, R⁹ and R¹⁰ are each C₁ -C₁₀ -alkyl, C₆ -C₁₅ -aryl or C₃ -C₁₀ -cycloalkyl, Y is nitrogen, phosphorus, arsenic, antimony or bismuth, Z is oxygen, sulfur, selenium or tellurium, n is an integer from 0 to 10, R⁵ is ##STR22## R¹¹ and R¹² are each hydrogen, C₁ -C₁₀ -alkyl, C₆ -C₁₅ -aryl or C₃ -C₁₀ -cycloalkyl, R¹³ and R¹⁴ are each C₁ -C₁₀ -alkyl, C₆ -C₁₅ -aryl or C₃ -C₁₀ -cycloalkyl, n¹ is an integer from 0 to 10, X¹ to X⁴ are each fluorine, chlorine, bromine, iodine, hydrogen, C₁ -C₁₀ -alkyl, C₆ -C₁₅ -aryl, alkylaryl having 1 to 10 carbon atoms in the alkyl radical and 6 to 20 carbon atoms in the aryl radical, --OR¹⁵ --, --NR¹⁵ R¹⁶ or ##STR23## R¹⁵ and R¹⁶ are each C₁ -C₁₀ -alkyl, C₆ -C₁₅ -aryl, alkylaryl, arylalkyl, fluoroalkyl or fluoroaryl, each having 1 to 10 carbon atoms in the alkyl radical and 6 to 20 carbon atoms in the aryl radical, R¹⁷ to R²¹ are each hydrogen, C₁ -C₁₀ -alkyl, 5-7-membered cycloalkyl which in turn may carry C₁ -C₁₀ -alkyl as a substituent, C₆ -C₁₅ -aryl or arylalkyl, and two adjacent radicals together may furthermore form a cyclic group of 4 to 15 carbon atoms, Si(R¹¹)₃, ##STR24## R²² is C₁ -C₁₀ -alkyl, C₆ -C₁₅ -aryl or C₃ -C₁₀ -cycloalkyl, R²³ and R²⁴ are each hydrogen, C₁ -C₁₀ -alkyl, C₆ -C₁₅ -aryl or C₃ -C₁₀ -cycloalkyl, R²⁵ and R²⁶ are each C₁ -C₁₀ -alkyl, C₆ -C₁₅ -aryl or C₃ -C₁₀ -cycloalkyl, n² is an integer from 0 to 10 and o, p, g, r are each an integer from 0 to 4, the sum o+p+q+r+1 corresponding to the valency of M, which was previously used as an active catalyst component in the preparation of polymers of C₂ -C₁₀ -alkenes, wherein the polymerization was stopped by adding an acid and the metallocene complex of the formula I was recovered by extraction from the reaction mixture, and B) a compound forming metallocene ions.
 2. A process as claimed in claim 1, wherein the C₂ -C₁₀ -alkene polymerized is ethylene. 